The proliferation of portable electronic devices such as cell phones and laptop computers has lead to an increased demand for high capacity, long endurance light weight batteries. Because of this, alkali metal batteries, especially lithium ion batteries, have become a useful and desirable energy source. Lithium metal, sodium metal and magnesium metal batteries are also well known and desirable energy sources.
By way of example and generally speaking, lithium batteries are prepared from one or more lithium electrochemical cells containing electrochemically active (electroactive) materials. Such cells typically include, at least, a negative electrode, a positive electrode, and an electrolyte interposed between the positive and negative electrodes.
Lithium ion batteries are well known. Lithium ion batteries have an insertion anode, such as a lithium metal chalcogenide, lithium metal oxide, coke or graphite. These types of electrodes are typically used with lithium-containing insertion cathodes to form an electroactive couple in a cell. The resulting cells are not charged in an initial condition. Before this type of cell can be used to deliver electrochemical energy, it must be charged. In the charging operation, lithium is transferred from the lithium-containing electrode cathode to the negative electrode. During discharge the lithium is transferred from the negative electrode back to the positive electrode. During a subsequent recharge, the lithium is transferred back to the negative electrode where it reinserts. Thus with each charge/discharge cycle, the lithium ions (Li+) are transported between the electrodes. Such rechargeable batteries are called rechargeable ion batteries or rocking chair batteries.
In order for the lithium ion battery to be successful it requires the use of an electrolyte that is highly conductive in order to sustain a high energy density. The performance of the lithium ion batteries is greatly affected by the quality of the electrolyte. Therefore, the battery industry is constantly attempting to improve the qualities and properties of electrolytes.
Conventional lithium ion batteries have employed liquid electrolytes. Such liquid electrolytes generally have relatively good ionic conductivities. However, such liquid electrolytes require the use of a physical separator to prevent electrical shorting which results in increased costs due to the need for separator material costs and extra processing costs. Additionally, such liquid electrolytes are subject to leakage, they restrict the feasible size and shape of the batteries, they can react chemically with the electrode components and they often exhibit electrochemical breakdown at voltages between 3V and above 4.5V.
Polymer electrolytes have been developed which are based on polymers and a conducting salt. Ion mobility through the electrolyte is possible through coordination of the lithium ion with suitable sites on the polymer chain. Many such conventional polymer electrolytes frequently have low ionic conductivities which do not meet the high demands needed to be met by modem batteries. Alternatively, such polymer electrolytes often lack dimensional stability which can be addressed by various modifications. However, often when modifications are made to improve dimensional stability ionic conductivity is impeded since conductivity requires a significant degree of polymer chain mobility.
Thus, alternative highly conductive electrolytes for use in modern batteries are constantly being sought. The crosslinked polymer electrolytes of the present invention are beneficial in that they are highly conductive, they have good chemical stability, they possess good mechanical properties, they have good thermal stability and they are of low toxicity. In addition, there is provided an economical and reproducible synthetic method for producing such electrolytes and batteries containing the electrolytes.